Make optional parts of LanguageInfo actually optional! (#553)

crates/amalthea/src/wire/language_info.rs

@@ -24,14 +24,14 @@ pub struct LanguageInfo {
     /// The file extension for script files in the language
     pub file_extension: String,
 
-    /// Pygments lexer (for highlighting), if different than name
-    pub pygments_lexer: String,
+    /// Pygments lexer (for highlighting), if different than `name`
+    pub pygments_lexer: Option<String>,
 
-    /// Codemirror mode (for editing), if different than name
-    pub codemirror_mode: String,
+    /// Codemirror mode (for editing), if different than `name`
+    pub codemirror_mode: Option<String>,
 
-    /// Nbconvert exporter, if not default
-    pub nbconvert_exporter: String,
+    /// Nbconvert exporter, if not the default 'script' exporter
+    pub nbconvert_exporter: Option<String>,
 
     /// Posit extension
     pub positron: Option<LanguageInfoPositron>,

crates/amalthea/tests/shell/mod.rs

@@ -93,9 +93,9 @@ impl ShellHandler for Shell {
             version: String::from("1.0"),
             file_extension: String::from(".ech"),
             mimetype: String::from("text/echo"),
-            pygments_lexer: String::new(),
-            codemirror_mode: String::new(),
-            nbconvert_exporter: String::new(),
+            pygments_lexer: None,
+            codemirror_mode: None,
+            nbconvert_exporter: None,
             positron: None,
         };
         Ok(KernelInfoReply {

crates/ark/src/shell.rs

@@ -160,9 +160,9 @@ impl ShellHandler for Shell {
             version: kernel_info.version.clone(),
             file_extension: String::from(".R"),
             mimetype: String::from("text/r"),
-            pygments_lexer: String::new(),
-            codemirror_mode: String::new(),
-            nbconvert_exporter: String::new(),
+            pygments_lexer: None,
+            codemirror_mode: None,
+            nbconvert_exporter: None,
             positron: Some(LanguageInfoPositron {
                 input_prompt: kernel_info.input_prompt.clone(),
                 continuation_prompt: kernel_info.continuation_prompt.clone(),

crates/ark/tests/kernel.rs

@@ -12,6 +12,9 @@ fn test_kernel_info() {
 
     assert_match!(frontend.recv_shell(), Message::KernelInfoReply(reply) => {
         assert_eq!(reply.content.language_info.name, "R");
+        assert_eq!(reply.content.language_info.pygments_lexer, None);
+        assert_eq!(reply.content.language_info.codemirror_mode, None);
+        assert_eq!(reply.content.language_info.nbconvert_exporter, None);
     });
 
     frontend.recv_iopub_busy();

crates/echo/src/shell.rs

@@ -69,9 +69,9 @@ impl ShellHandler for Shell {
             version: String::from("1.0"),
             file_extension: String::from(".ech"),
             mimetype: String::from("text/echo"),
-            pygments_lexer: String::new(),
-            codemirror_mode: String::new(),
-            nbconvert_exporter: String::new(),
+            pygments_lexer: None,
+            codemirror_mode: None,
+            nbconvert_exporter: None,
             positron: None,
         };
         Ok(KernelInfoReply {